1) Field of the Invention
The invention is in the field of Microelectromechanical Systems (MEMS).
2) Description of Related Art
For the past several years, MEMS structures have been playing an increasingly important role in consumer products. For example, MEMS devices, such as sensors, detectors and mirrors, can be found in products ranging from air-bag triggers in vehicles to displays in the visual arts industry. In another example, high quality MEMS oscillators may be used in place of crystal oscillators to keep track of time and to provide a stable clock signal for digital integrated circuits. As these technologies mature, the demands on precision and functionality of the MEMS structures have escalated. For example, optimal performance may depend on the ability to fine-tune the characteristics of various components of these MEMS structures. Furthermore, consistency requirements for the performance of MEMS devices (both intra-device and device-to-device) often dictate that the processes used to fabricate such MEMS devices need to be extremely sophisticated.
Many devices, particularly MEMS devices, do not function properly when embedded in a completely solid environment. For example, a MEMS device may include a resonator or accelerometer fabricated on a substrate, each of which includes at least one element that must mechanically move relative to the substrate during operation. Freedom to move during operation would be lost if these elements were simply left embedded in a solid film deposited over the substrate, as is commonly done in the microelectronics industry. For this reason, a micromechanical structure must be released from the substrate so that it is not contained within a purely solid environment. However, a released micromechanical structure is fragile and must be protected with some form of package which isolates a microenvironment surrounding the micromechanical structure from a global environment surrounding the substrate. The package may further be hermetically sealed so that it can remain evacuated or pressurized with a gas or other fluidic media. One option is encapsulating a device in a conventional “TO can,” well-known in the industry as a standard packaging method for a discrete device. However, this type of packaging is not wafer-level and is limited to stand-alone (discrete) devices, and therefore is expensive.
Thus, an encapsulated MEMS device and a method to form an encapsulated MEMS device are described herein.